To ensure low power consumption in a sleep mode, a microcontroller may be switched to a very low frequency system clock provided by an internal or external oscillator. A conventional 32 KHz oscillator consumes about one microampere and the power budget for an entire system in an industry standard deep sleep mode is one (1) microampere. In order to meet this industry standard deep sleep requirement, the oscillator has to consume less than 150 nanoamperes, including bias generation, and still be able to support a wide range of crystals. With such a wide variation of crystal quality (RESR from about 30 kilohms to about 90 kilohms) based upon temperature, a crystal oscillator will not start or cannot sustain oscillation at such low current values. Lower power crystal oscillators, approximately 200 nanoamperes, will only work with very low ESR crystals that are expensive and not readily available.